1. Field of the Invention
This invention relates to a radiation image pickup device and a radiation image pickup system for taking a one-dimensional or two-dimensional image of an object that can suitably be used for a medial instrument, a non-destructive tester or the like.
2. Related Background Art
To begin with, an X-ray imaging apparatus will be described below as typical radiation image pickup device for picking up an image of an object obtained by exposing the object to radiation.
With an X-ray imaging apparatus, a visible image of the object is produced by converting the X-ray image picked up by the image pickup element of the apparatus into electric signals. Since X-rays show a high energy level when compared with rays of visible light, the image pickup element cannot absorb all the X-rays irradiated in the X-ray imaging apparatus and hence some X-rays that have been transmitted through the image pickup element can enter one or more than one semiconductor integrated circuits of the peripheral circuits of the image pickup element to make the latter give rise to operation errors.
In view of this problem, U.S. Pat. No. 5,777,335 and Japanese Patent Application Laid-Open No. 9-152486 propose in their specifications and drawings an arrangement of providing an X-ray imaging apparatus with a shielding member typically made of lead for shielding the semiconductor integrated circuits of the apparatus from X-rays.
FIG. 16 of the accompanying drawings schematically illustrates such a known radiation image pickup device. Referring to FIG. 16, there are shown an image pickup element 1, a support 2 for supporting the image pickup element and other members, a circuit substrate 3, a radiation shielding member 4 typically made of lead, semiconductor integrated circuit elements 5, a cabinet 11, a flexible wiring substrate 12 and radiation 13.
Radiation emitted from a radiation source (not shown) is transmitted through an object and enters the radiation image pickup device. The radiation 13 entering the radiation image pickup device contains X-ray information on the object.
The X-rays entering the image pickup element 1 and containing information on the object generates directly or indirectly an electric charge in the element 1, which electric charge can be read out by an electronic circuit as electric signal.
Since X-rays show a high energy level when compared with rays of visible light so that all the X-rays that enter the image pickup element are not completely absorbed by the latter and hence some of the X-rays can be transmitted through the image pickup element 1. Therefore, the shielding member 4 that is typically a plate of lead is arranged at the side (rear side) opposite to the light receiving side of the image pickup element 1 to prevent X-rays from entering the circuit substrate 3 carrying semiconductor integrated circuit elements 5.
With the arrangement of FIG. 16, the image pickup device contains a lead plate 4 having a surface area significantly larger than the circuit substrate 3 to be shielded from X-rays to make the entire device rather heavy. While such a heavy weight may be allowed to a large medical X-ray apparatus for taking an X-ray picture of a standing or lying subject, it cannot meet the requirements of portable radiation image pickup apparatus for use in a doctor consultation room, at the bed side of a patient or in an ambulance, for which the demand has been rising rapidly in recent years.
In view of the above identified circumstances, it is therefore an object of the present invention to provide a radiation image pickup device and a radiation image pickup system that are lightweight and highly reliable. Another object of the present invention is to provide a radiation image pickup device and a radiation image pickup system that can hardly give rise to operation errors if the peripheral circuits are exposed to radiation.
In an aspect of the invention, the above objects are achieved by providing a radiation image pickup device comprising an image pickup element for converting radiation into an electric signal and picking up an image of an object, a circuit substrate electrically connected to the image pickup element and provided with at least either a circuit for controlling the input signal to the image pickup element or a circuit for processing the output signal from the image pickup element, active elements arranged on the circuit substrate and constituting the circuit and radiation shielding members for shielding the active elements from radiation, the radiation shielding members having a surface area smaller than that of the circuit substrate.
Active elements such as semiconductor integrated circuits mounted on a circuit substrate are mostly arranged in a distributed manner and the gaps separating neighboring elements are not uniform. For example, a semiconductor integrated circuit showing a square profile may have a side as short as several millimeters or as long as several centimeters.
Therefore, according to the invention, the shielding members are made to have a surface area smaller than that of the circuit substrate and arranged in a distributed manner so that each one of them covers a single active element in principle, although some of the shielding members may cover at least several active elements. With this arrangement, it is possible to make the image pickup device lightweight.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention include flat members, each of which is adapted to be commonly used for a plurality of active elements. With such an arrangement, it will be not necessary to use too small shielding members for shielding so many small elements such as discrete semiconductor elements and hence the efficiency of assembling a radiation image pickup device according to the invention will be greatly improved.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention include flat members, each of which is adapted to be used only for a semiconductor integrated circuit element operating as active element and has a surface area greater than the corresponding semiconductor integrated circuit element. For the purpose of the present invention, the term xe2x80x9cflat membersxe2x80x9d may include plate-like, sheet-like and/or film-like ones.
Alternatively, the radiation shielding members of a radiation image pickup device according to the invention may include flat members, each of which is adapted to be used only for a semiconductor integrated circuit element operating as active element and has a surface area equal to or greater than the package of the corresponding semiconductor integrated circuit element.
Still alternatively, the radiation shielding members of a radiation image pickup device according to the invention may include flat members, each of which is adapted to be used only for a semiconductor integrated circuit element operating as active element and has a surface area smaller than the package of the corresponding semiconductor integrated circuit element but greater than the semiconductor chip of the semiconductor integrated circuit element. With such an arrangement, the overall radiation image pickup device according to the invention can be made more lightweight.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention are arranged between the circuit substrate and the image pickup element and separable from the circuit substrate. With such an arrangement, the shielding members can be removed with ease from the device when the device is thrown away as waste.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention are arranged in contact with the circuit substrate.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention are arranged on the side of the circuit substrate opposite to the side where the active elements are mounted.
Alternatively, the radiation shielding members of a radiation image pickup device according to the invention may be arranged on the side of the circuit substrate where the active elements are mounted.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention are formed by means of a solder applied to the circuit substrate.
Preferably, the image pickup element of a radiation image pickup device according to the invention is provided with a scintillator adapted to emit a visible light upon receiving radiation and an photoelectric converter adapted to generate an electric signal upon receiving said visible light.
Alternatively, the image pickup element of a radiation image pickup device according to the invention may be provided with a converter adapted to generate an electric signal upon receiving radiation.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention is so designed as to have a thickness sufficient for blocking the radiation attenuated when transmitted through the image pickup element.
In another aspect of the invention, there is provided a radiation image pickup device comprising an image pickup element for converting radiation into an electric signal and picking up an image of an object and a flexible circuit substrate having semiconductor integrated circuit chips electrically connected to the image pickup element and bent by an angle not smaller than 90xc2x0 relative to the image pickup plane of the image pickup element, the flexible circuit substrate being provided with radiation shielding members for shielding semiconductor integrated circuit chips from radiation.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention are arranged either on the front surface side or on the rear surface side of the flexible circuit substrate.
Preferably, the flexible circuit substrate of a radiation image pickup device according to the invention is bent in such a way that the semiconductor integrated circuit chips are located on the rear surface of the image pickup element and the radiation shielding members are arranged between the image pickup element and the semiconductor integrated circuit chips.
In still another aspect of the invention, there is provided a radiation image pickup device comprising an image pickup element for converting radiation into an electric signal and picking up an image of an object, a circuit substrate electrically connected to the image pickup element and provided with at least either a circuit for controlling the input signal to the image pickup element or a circuit for processing the output signal from the image pickup element, semiconductor integrated circuit elements arranged on the circuit substrate to constitute the circuit and radiation shielding members for shielding the semiconductor integrated circuit elements from radiation, each of the radiation shielding members being adapted to be used only for a semiconductor integrated circuit element and having a surface area smaller than the package of the corresponding semiconductor integrated circuit element but greater than the semiconductor chip of the semiconductor integrated circuit element.
In still another aspect of the invention, there is provided a radiation image pickup device comprising an image pickup element for converting radiation into an electric signal and picking up an image of an object, a circuit substrate electrically connected to the image pickup element and provided with at least either a circuit for controlling the input signal to the image pickup element or a circuit for processing the output signal from the image pickup element, active elements arranged on the circuit substrate to constitute the circuit and radiation shielding members for shielding the active elements from radiation, the radiation shielding members including a solder layer arranged on the circuit substrate and having a surface area smaller than that of the circuit substrate but greater than the area of the mounted active elements.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention contain at least a metal selected from Pb, Ta, Ba and W or an alloy of any of them.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention contain a plurality of solder balls.
Alternatively, the radiation shielding members of a radiation image pickup device according to the invention may be made of hardened organic resin containing at least a metal selected from Pb, Ta, Ba and W.
Preferably, the radiation shielding members of a radiation image pickup device according to the invention contain powder of a material effective for blocking radiation.
In still another aspect of the invention, there is provided a radiation image pickup system comprising a radiation image pickup device according to the invention and a display for displaying the image picked up by the radiation image pickup device.